There is a growing awareness of the hazards to which individuals such as miners, factory workers and others are exposed during the extended periods of time which they spend in atmospheres containing airborne particulate matter (e.g. asbestos, silicates, ceramics) or a variety of gases. This arises particularly in connection with industrial workers. Employers may even be subject to heavy legal liability years after employee exposure to harmful substances. There is therefore a need to monitor the quality of the air which such an individual is breathing over a period of time, so as to be able to determine its quality, and its content of potentially harmful constituents.